Conventional gun systems, and particularly such gun systems as are utilized in helicopters, other aircraft and air defense gun systems, where the operator is "in the loop" for at least a portion of the functioning modes of the system, have conventionally not provided for closed-loop aim error correction. In some instances, the operator may be provided with a visual indication of the projected line of flight for the projectile, in a "heads- up display", to enable more accurate manual aiming. However, to date, such aiming systems have not been capable of achieving aim accuracies much less than 10 milliradians.
The search for more accurate gun aiming systems has led to the proposal or development of various closed-loop error correction systems for use in anti-aircraft and other gun systems. Such closed-loop systems have usually been based on the use of radar to track the target and to measure the angle between target centroid and bullet path centroid at the target's range. However, radar closed-loop gun control systems are relatively complex and high in cost, and further, may impose an excessive weight penalty in certain applications. Additionally, radar closed-loop systems cannot be easily adapted to include gunner observations in the fire control sequence. Finally, such systems are particularly deficient when severe ground clutter environments are encountered.
Thus, it is desirable to have a closed-loop gun control system that is relatively light in weight and low in cost. Such a closed-loop system is particularly desirable when it provides an accuracy improvement over the 10 milliradian accuracy available with conventional aiming techniques and which is passive so as not to provide signals that may be utilized by opposing forces to neutralize the gun system.